X-ray crystallographic investigations and molecular modeling techniques will be used to obtain structural information for hemerythrin and other metalloproteins containing binuclear iron complexes. Several other proteins, purple acid phosphatase, uteroferrin and a ribonucleotide reductase, contain iron complexes similar to the one we have most fully characterized in the invertebrate respiratory protein, hemerythrin. These molecules all make use of the chemical properties of the iron complex in carrying out biological functions ranging from oxygen transport (hemerythrin) to the synthesis of nucleic acid components (ribonucleotide reductase). The goal of this research project is to determine the structures of various forms of hemerythrin to explain the molecule's functional properties in terms of the structural information, with special emphasis on the metal center. Single crystal diffraction studies of oxy and deoxyhemerythrin, extended to high resolution (2.0 angstrom or higher), will provide a structural view of reversible oxygenation, while crystallographic analyses of o-phosphoryl ethanolamine and sulfido derivatives of hemerythrin will pinpoint changes associated with binding of allosteric effectors and changes in the oxidation states of the iron atoms. Subunit interactions found in a structure determination of a dimeric hemerythrin, when compared with studies of hemerythrin octamers and trimers carried out in this and other laboratories. will show how changes in the intersubunit contacts lead to different oligomeric forms. Models of the redox complex between hemerythrin and cytochrome b5, generated and analyzed using computer graphics and energy minimization techniques, will allow investigation of elements involved in and controlling electron transfer. Finally, the structure determination of a bacterial protein, rubrerythrin, containing one binuclear iron complex as well as two rubredoxin-like complexes per dimer, will lead to the identification of the ligands for the metals as well as the structure of the protein. The research proposed here will contribute to our understanding of the role of non-heme iron in biological systems, especially the role of the binuclear iron centers containing mu-oxygen and carboxylate bridges.